• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.4
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• pp.315-326
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• 2024

In this study, the Delphi method and AHP (analytic hierarchy process) were used to evaluate tunnel collapse risk from a comprehensive and multifaceted perspective. Influence factors were established through literature reviews, previous studies, and brainstorming sessions with expert groups, resulting in the construction of five main classification systems. A panel of 21 experts was formed, and three rounds of Delphi surveys were conducted to prevent errors and biases in the expert judgment process, thereby enhancing reliability. Ultimately, 14 influence factors were identified through CVR (content validity ratio) and COV (coefficient of variation) analyses of the experts' responses. Subsequently, the AHP method was applied to assess the relative importance of each influence factor and calculate the final composite weights. The timing of support and reinforcement had the highest priority, followed by groundwater inflow, joint conditions, support pattern levels, and auxiliary methods. These findings help identify the key factors affecting tunnel collapse risk and provide a foundation for developing strategies to improve tunnel safety.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.9 no.4
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• pp.113-122
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• 2010

Research and development related to advanced railway systems is currently underway presently to promote the maintenance and economic feasibility of subways, and the aim of such research and development is to enhance the functionality, passenger convenience, system safety and reliability assurance of the subway. In this situation, a study that predicts the effect that the development of such an advanced railway system would have on subway users is required. To this end, this study derived willingness to pay and decision factors with the introduction of an advanced railway system after surveying passengers who use subway lines 1~8. The Price Sensitivity Method (PSM) was applied to derive the willingness to pay in relation to user convenience (operating speed, ride comfort, safety, comfort, security and informativeness) with the introduction of an advanced railway system. In addition, willingness to pay and decision factors were examined after explaining the effects of introducing an advanced railway system in detail to subway users. Through the analysis, it was found that willingness to pay amounted to a premium of 148 won ~ 161 won with the introduction of an advanced railway system, and that this was affected by factors such as gender, frequency of use, satisfaction with comfort, and satisfaction with security.

• Fire Science and Engineering
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• v.31 no.2
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• pp.52-60
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• 2017

Numerical simulations were performed to evaluate the habitability of an operator for a cabinet fire in the main control room of a nuclear power plant presented in NUREG-1934. To this end, a Fire Dynamics Simulator (FDS), as a representative fire model, was used. As the criteria for determining the habitability of operator, toxic products, such as CO, were also considered, as well as radiative heat flux, upper layer temperature, smoke layer height, and optical density of smoke. As a result, the probabilities of exceeding the criteria for habitability were evaluated through the sensitivity analysis of the major input parameters and the uncertainty analysis of fire model for various fire scenarios, based on V&V (Verification and Validation). Sensitivity analyses of the maximum heat release rate, CO and soot yields, showed that the habitable time and the limit criterion, which determined the habitability, could be changed. The present methodology will be a realistic alternative to enhancing the reliability for a habitability evaluation in the main control room using uncertain information of cabinet fires.

• Fire Science and Engineering
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• v.30 no.5
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• pp.67-73
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• 2016

This paper examined the structure, fire resistance of brass fittings type CSST employed in gas appliances and the reliability verification. Brass fittings of type CSST consisted of cladding, tubing, nut, clamp ring, socket, and ball valve. The applicable JIA standard regulates the maximum working pressure to be 4.2 kPa, which is the highest pressure of the relevant standards and the KS D 3625 stipulates the maximum pressure to be 3.24 kPa. With a normal product, the average resistance within the confidence interval was found to be $7.36m{\Omega}$. The average resistance within the confidence interval was $6.67m{\Omega}$ after the fire resistance tests. The analysis indicated that the AD was 1.584 and the standard deviation was 0.3972 with respect of a normal product. Compared to the normal product, however, the damaged product after the fire resistance test showed better features, such as an AD of 1.145 and a standard deviation of 0.2467. Moreover, the average resistance of the normal product was $7.359m{\Omega}$ and the standard deviation in histogram analysis was 0.3972. The average resistance of the damaged product after the fire resistance test in the histogram was $6.67m{\Omega}$ and the standard deviation was 0.2467.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.2
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• pp.133-139
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• 2013

Morphing aircraft capable of varying their wing form can operate efficiently at various flight conditions. However, radical morphing of the aircraft leads to increased structural complexities, resulting in occurrence of dynamic instabilities such as flutter, which can lead to catastrophic events. Therefore, it is of utmost importance to investigate and understand the changes in flutter characteristics of morphing wings, to ensure uncompromised safety and maximum reliability. In this paper, a study on the flutter characteristics of the folding wing type morphing concept is conducted, to examine the effect of changes in folding angles on the flutter speed and flutter frequency. The subsonic aerodynamic theory Doublet Lattice Method (DLM) and p-k method are used, to perform the flutter analysis in MSC.NASTRAN. The present baseline flutter characteristics correspond well with the results from previous study. Furthermore, enhancement of the flutter characteristics of an aluminum folding wing is proposed, by varying the outboard wing folding angle independently of the inboard wing folding angle. It is clearly found that the flutter characteristics are strongly influenced by changes in the inboard/outboard folding angles, and significant improvement in the flutter characteristics of a folding wing can be achieved, by varying its outboard wing folding angle.

• Journal of Korean Neurosurgical Society
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• v.52 no.3
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• pp.204-209
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• 2012

Objective : The authors performed a retrospective study to assess the accuracy and clinical benefits of a navigation coupled with O-arm$^{(R)}$ system guided method in the thoracic and lumbar spines by comparing with a C-arm fluoroscopy-guided method. Methods : Under the navigation guidance, 106 pedicle screws inserted from T7 to S1 in 24 patients, and using the fluoroscopy guidance, 204 pedicle screws from T5 to S1 in 45 patients. The position of screws within the pedicle was classified into four groups, from grade 0 (no violation cortex) to 3 (more than 4 mm violation). The location of violated pedicle cortex was also assessed. Intra-operative parameters including time required for preparation of screwing procedure, times for screwing and the number of X-ray shot were assessed in each group. Results : Grade 0 was observed in 186 (91.2%) screws of the fluoroscopy-guided group, and 99 (93.4%) of the navigation-guided group. Mean time required for inserting a screw was 3.8 minutes in the fluoroscopy-guided group, and 4.5 minutes in the navigation-guided group. Mean time required for preparation of screw placement was 4 minutes in the fluoroscopy-guided group, and 19 minutes in the navigation-guided group. The fluoroscopy-guided group required mean 8.9 times of X-ray shot for each screw placement. Conclusion : The screw placement under the navigation-guidance coupled with O-arm$^{(R)}$ system appears to be more accurate and safer than that under the fluoroscopy guidance, although the preparation and screwing time for the navigation-guided surgery is longer than that for the fluoroscopy-guided surgery.

• The Journal of the Society of Korean Medicine Diagnostics
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• v.15 no.2
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• pp.203-214
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• 2011

Objectives: The objective of the current study is to determine whether an ultrasound device system is adequate for measuring distance from the abdominal surface of Sangwan (CV13) to peritoneum in front of anterior surface of liver. Methods: We recruited 3 healthy young male subjects and 2 sonographers. The each sonographer measured vertical shortest distance from the abdominal surface of Sangwan (CV13) to peritoneum in front of anterior surface of liver with a ultrasound device with three methods of 3.5 MHz convex probe and gel, 9 MHz linear probe and gel, and 9 MHz linear probe and solid gel pad, three times in random order. Because the total variation could be divided into repeatability, reproducibility and subject-to-subject variation in Gage R&R method, we compared the sources of variation associated with the measurement system with an analysis of variance model. Results & Conclusions: Number of distinct categories is calculated on the basis of standard deviation of subject-to-subject divided by standard deviation of total Gage R&R. If the number of categories is five or more, the measurement system may be acceptable for the analysis of the process. The number of distinct categories of the ultrasound device system for measuring distance from the abdominal surface of Sangwan (CV13) to peritoneum in front of anterior surface of liver were 9.20 (9 MHz linear probe and gel), 14.70 (9 MHz linear probe and solid gel pad). So we concluded that repeatabilities and reproducibilities of the ultrasound device system for measuring distance from the abdominal surface of Sangwan (CV13) to peritoneum in front of anterior surface of liver with the methods of 9 MHz linear probe and gel, and 9 MHz linear probe and solid gel pad were acceptable.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.1
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• pp.67-77
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• 2018

The objective of this study is to extract the shape of the slope from the images acquired using UAV and evaluate its suitability and reliability when applied to slope stability analysis. UAV is relatively inexpensive and simple, and it is possible to make terrain survey by generating point clouds. However, the image acquired from UAV can not be directly photographed by the forest canopy due to the influence of trees, resulting in severe distortion of the terrain. In this study, therefore, the effects of forest canopy were verified and the slope stability analysis was performed. Images acquired in winter and summer were used, because summer images are heavily influenced by the forest canopy and winter images are not. As a result of the study, the winter image is suitable for the extraction of slope shape, but severe terrain distortion occurs in the summer image. Therefore, slope stability analysis using slope shape extracted from summer image is impossible, so it should be modified for slope stability analysis. The modified slope did not completely eliminate the distortion of the terrain, but it could express the approximate shape of the slope. As a result of the slope stability analysis, the location and shape of the failure surface are the same, and the error of the safety factor is less than 0.2, which is close to the actual slope.

• Geomechanics and Engineering
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• v.5 no.4
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• pp.363-377
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• 2013

Any structure constructed on the earth is supported by the underlying soil. Foundation is an interfacing element between superstructure and the underlying soil that transmits the loads supported by the foundation including its self weight. Foundation design requires evaluation of safe bearing capacity along with both immediate and long term settlements. Weak and compressible soils are subjected to problems related to bearing capacity and settlement. The conventional method of design of footing requires sufficient safety against failure and the settlement must be kept within the allowable limit. These requirements are dependent on the bearing capacity of soil. Thus, the estimation of load carrying capacity of footing is the most important step in the design of foundation. A number of theoretical approaches, in-situ tests and laboratory model tests are available to find out the bearing capacity of footings. The reliability of any theory can be demonstrated by comparing it with the experimental results. Results from laboratory model tests on square footings resting on sand are presented in this paper. The variation of bearing capacity of sand below a model plate footing of square shape with variation in size, depth and the effect of permissible settlement are evaluated. A steel tank of size $900mm{\times}1200mm{\times}1000mm$ is used for conducting model tests. Bearing capacity factor $N_{\gamma}$ is evaluated and is compared with Terzaghi, Meyerhof, Hansen and Vesic's $N_{\gamma}$ values. From the experimental investigations it is found that, as the depth of sand cushion below the footing ($D_{sc}$) increases, ultimate bearing capacity and settlement values show an increasing trend up to a certain depth of sand cushion.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.4
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• pp.671-686
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• 2018

Recently, earthquakes have occurred near Gyeongju and Pohang and the social demands are thus being increased for seismic analysis of tall buildings and their adjacent underground structure in big cities. Since most of the previous seismic analysis studies considered a tall building and an adjacent underground structure separately, however, they lack the analysis on dynamic mutual behavior between two structures. Therefore, in this study, a dynamic analysis with a full soil-structure interaction was performed for a complex underground facility with a tall building and an adjacent underground structure constructed on the bedrock with a surface layer. To improve the reliability, in particular, a pseudo-static analysis was performed and compared with the dynamic analysis results. It is comprehensively concluded that the analysis of adjacent underground structures being considered is more conservative than that of not considered.